In the art of drilling wellbores for the purpose of producing hydrocarbon bearing formations found downhole therein, it is often advantageous to slant the lower marginal end of the borehole so that the pay zone is penetrated substantially horizontally and at a considerable distance radially away from the drilling rig. One of the advantages found in slanting a borehole in this manner is to enable the pay zone to be entered at a number of different locations radially spaced about the drilling rig so that a plurality of the boreholes can be formed from a common drilling location. This technique is especially advantageous when the cost of moving the drilling rig is considerable, as for example, an offshore drilling rig.
Another advantage derived from slanting the lower marginal end of the borehole horizontally respective to the pay zone is that a tremendous amount of surface area of the borehole is located directly in the pay zone; and therefore, a greater number of perforations can be formed which extend back up into the hydrocarbon bearing formation, thereby achieving a much greater production rate from the pay zone.
Where the pay of the slanted borehole is located in an unconsolidated type strata, the loose particles of the formation tend to flow through the perforations and thereby bring about many undesirable and complicated production problems which are difficult to overcome. Accordingly, it would be desirable to be able to perforate a slanted borehole in such a manner that the formation is penetrated only in a predominately downward direction; and accordingly, flow of unconsolidated material must therefore occur in an upward direction, thereby causing the solid matter which constitutes the pay zone to tend to gravitate downwardly and remain insitu respective to the formation, and this is the primary subject of this invention.